Abrasive Disk, Hand-Held Power Tool and Control Method

ABSTRACT

An abrasive disk has one or more layers in which abrasive grains are embedded. Embedded in one layer is a sensor for detecting an original periphery of the abrasive disk that has been altered by wear. The sensor has at least one closed conductor loop which is arranged at a radial distance from the original periphery such that, when the original periphery is worn by more than the radial distance, the conductor loop is interrupted. A transponder emits a radio signal indicative of whether the conductor loop is closed or interrupted.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of PCT International ApplicationNo. PCT/EP2018/079648, filed Oct. 30, 2018, which claims priority under35 U.S.C. § 119 from European Patent Application No. 17201070.4, filedNov. 10, 2017, the entire disclosures of which are herein expresslyincorporated by reference.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to a disk, a hand-held power tool forabrasive disks and a control method.

Abrasive disks rotate at high speed. During use of the disk, abradedmatter of the disk and of the machined material fly away from the diskat high speed. Furthermore, the disk is subject to high loads due tocentrifugal force. For safety reasons, therefore, the regulatoryauthorities set an upper limit for the rotational speed.

Abrasive disks are subject to wear. The wear leads to a reducedperiphery and thus reduced rotational speed. The reduced rotationalspeed adversely affects the machining performance of the disks.

An abrasive disk according to the invention has one or more layers, inwhich abrasive grains are embedded. Embedded in one layer is sensor fordetecting an original periphery of the abrasive disk that has beenaltered by wear. The sensor has at least one closed conductor loop,which is arranged at a radial distance from the original periphery suchthat, when the original periphery is worn by more than the radialdistance, the conductor loop is interrupted. A transponder emits a radiosignal indicative of whether the conductor loop is closed orinterrupted.

The radio signals indicate the radial wear of the disk. A hand-heldpower tool can adjust the speed accordingly.

A hand-held power tool for the abrasive disk has a holder for theabrasive disk, an electric motor for rotating the abrasive disk and aspeed control for the electric motor. A communication device is set upto receive the radio signal emitted by the transponder of the abrasivedisk. A device controller sets the speed for the speed control based onthe radio signal received.

The following description explains the invention on the basis ofexemplary embodiments and Figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an electric angle grinder;

FIG. 2 shows an abrasive disk in cross section;

FIG. 3 shows the abrasive disk in a plan view;

FIG. 4 shows a detail of an abrasive disk; and

FIG. 5 shows a detail of an abrasive disk.

DETAILED DESCRIPTION OF THE DRAWINGS

identical or functionally identical elements are indicated by the samereference numerals in the Figures, unless stated otherwise.

FIG. 1 shows an electric hand-held power tool 1 for abrasive disks 2.The hand-held power tool 1 has a tool holder 3 for an abrasive disk. 2The tool holder 3 is coupled to an electric motor 4, which rotatablydrives the tool holder 3 about its axis. A speed control 5 controls theelectric motor 4. The speed control 5 limits the speed to a maximumspeed in order to prevent damage to the abrasive disk 2 and possibleinjury to the user. A protective hood 6 annularly encloses more thanhalf of the tool holder 3, in order to protect the user from flyingsparks and substance abrasively removed. The hand-held power tool 1 hasa handle 7 with which the user can hold and guide the hand-held powertool 1 in operation. At or near the handle 7, a button 8 for startingthe electric motor 4 is arranged. The hand-held power tool 1 can bepowered from the grid or by means of batteries 9.

The hand-held power tool 1 has a device controller 10. Among otherthings, the device controller 10 sets the target speed for the speedcontrol 5. The device controller 10 may access a memory 11, in which atarget speed is stored. The device controller 10 may also access acommunication device 12 in order to communicate with an abrasive disk 2.The communication device 12 has a transmitter 13 for transmittingradio-based signals and a receiver 14 for receiving a radio-basedresponse of the abrasive disk 2. A transmission power of the transmitter13 is preferably sufficient to power a transponder, e.g., aradio-frequency identification (RFID) chip, without its own energysource via the transmission power.

When the button 8 is actuated, the device controller 10 directs arequest to the disk 2 to identify it. The disk 2, if equipped with atransponder 15, reports an identification number or type number. Thedevice controller 10 checks whether the type number differs from thedisk 2 last used. If this is the case, the device controller 10 inquireswhat is a maximum permissible speed for the disk 2. The devicecontroller 10 stores the maximum permissible speed in the memory 11.Preferably, the disk 2 transmits a list of different maximum speeds tobe used depending on a degree of wear of the disk 2. The degree of wearis coded in radio signals which are transmitted in the list. The devicecontroller 10 stores the list in the memory 11. The device controller 10sets the speed of the speed control 5 to the maximum permissible speedthat corresponds to the current degree of wear. The device controllerinquires at intervals via the communication device 12 what is the degreeof wear of the disk 2. The radio signal received as a response by thecommunication device 12 is compared with the stored list. The maximumpermissible speed associated with the radio signal is transmitted to thespeed control 5.

FIG. 2 schematically shows an embodiment of an abrasive disk 2 in crosssection. The abrasive disk 2 shown is a multi-layer cutting disk withdifferent grains. The abrasive disk 2 has a middle layer 16 with firstgrains. The middle layer 16 can be produced for example by anelectrodeposited matrix in which the grains are distributed. The twoouter layers 17, 18 can also be produced with an electrodeposited matrixand scattered embedded grains. The grains of the middle layer 16 may belarger than the grains of the outer layers 17, 18. The grains given byway of example have a diameter of 4 μm to 10 μm and 10 μm to 20 μm,respectively. The production of the layers 18 is purely exemplary.Another method given by way of example is based on fabrics that areimpregnated with resins mixed the grains. The resins are then cured. Thenumber of different layers is also purely exemplary. Other disks haveone, two or more different abrasive layers. Typically, the disks 2 areprovided with a cover layer 19, on which the disk type, manufacturer,etc. are indicated.

The disks are produced with different diameters. Diameters given by wayof example are 8.9 cm and 11.2 cm. FIG. 3 illustrates an instance ofwear given by way of example. The as-new disk 2 has the originalperiphery 20. The disks 2 become worn during use, which reduces thediameter and periphery. Examples of a periphery 21 of a worn disk 2 areshown by dashed lines. In the following, the original diameter, originalradius or original periphery 20 designates the respective property of anew, unused abrasive disk 2.

Embedded in the abrasive disk 2 is a sensor 22, which detects wear andthe degree of wear of the disk 2. The sensor 22 is based on one or moreclosed conductor loops 23, 24. The conductor loops 23, 24 run parallelto the abrasive layers 16. For example, the conductor loop 23 may beprinted on a film of non-conductive plastic. The film is stacked as afurther layer 25 with the other layers 16. The film may be arranged asshown on the abrasive layers 16 or between the abrasive layers 18. Theconductor loops 23, 24 have a low mechanical strength. The conductorloops 23, 24 preferably have a height of less than 100 μm. The conductorloops 23, 24 are preferably made of copper or graphite.

The closed conductor loop 23 has a (detection) portion 26 which isclosest to the periphery 20 and farthest from a center of the disk 2.The detection portion 26 is at a radial distance 27. The detectionportion 26 given by way of example lies within the original periphery 20and outside a worn periphery 21. The radius of the worn periphery 20corresponds to the original radius reduced by the distance 27. As thedisk 2 becomes worn, the detection portion 26 is exposed by the distance27, i.e., up to the worn periphery 21, and destroyed. The previouslyclosed conductor loop 23 is then interrupted.

Preferably arranged on the disk 2 is a sensor 22, for example on in thelayer 25 with the conductor loops. The sensor 22 may be realized forexample as an RFID chip. The sensor 22 checks the closed or interruptedstate of the conductor loop 23. The sensor 22 determines the electricalproperties of the conductor loop 24, e.g., resistivity, inductance andelectromagnetic resonant frequency. The sensor 22 is based for exampleon an ohmmeter for determining the electrical resistance value of theconductor loop 23. If the resistance value exceeds a threshold value,e.g., 1 megohm, the conductor loop 24 is considered to be interrupted,otherwise the conductor loop 23 is considered to be closed. Theconductor loop 23 is galvanically connected to the sensor 22. Theohmmeter applies a voltage to the conductor loop 23 and measures theamplitude of the current flowing in the conductor loop 23. Anotherconfiguration of the sensor 22 determines the inductance of theconductor loop 23. A further configuration of the sensor 22 determineswhether the resonant frequency of the conductor loop 23 changes. Theconductor loop 23 may be part of an electrical oscillating circuit or beinductively coupled to an oscillating circuit of the sensor 22. Whilethe conductor loop 23 or the oscillating circuit can be excited at apredetermined resonant frequency with a closed conductor loop 23, thisis not possible with an interrupted conductor loop, or if it is at adifferent resonant frequency. The sensor 22 excites the oscillatingcircuit at the predetermined resonant frequency. If the powerconsumption exceeds a threshold value due to the resonant excitation,the conductor loop 23 is considered to be closed, otherwise it isconsidered to be interrupted. The described configurations fordetermining the electrical properties of the conductor loop 23 are givenby way of example. The sensor 22 may also be passively formed. Anexternal transmission source excites the oscillating circuit 28.

The sensor 22 includes a transponder 15. The transponder 15 may consistof a passive antenna. The transponder 15 transmits the state of theconductor loop, i.e., whether the conductor loop is interrupted orwhether the conductor loop is closed.

In one configuration, the sensor 22 includes a memory 29, in whichcharacteristics of the abrasive disk 2 are stored. For example, amaximum permissible speed for the disk 2 when the conductor loop 23 isclosed and a maximum permissible speed for the disk 2 when the conductorloop 23 is interrupted are stored in the memory 29. The sensor 22determines the currently permissible rotational speed based on thedetermined state of the conductor loop 23. The permissible speed isoutput via the transponder 15. In one configuration, the transponder 15can transmit both values, i.e., for the closed conductor loop 23 and theinterrupted conductor loop 23, at one time to the communication device12 of the hand-held power tool 1. At the same time, the transponder 15transmits the radio signals or their coding for the two states. Anevaluation can thus be transmitted to the device controller 10.

In addition to the first conductor loop 23 described, the sensor 22 mayhave a. second conductor loop 24 or a number of conductor loops. Thesecond conductor loop 24 is at a greater distance 30 from the originalperiphery 20. Accordingly, the second conductor loop 24 is only severedwhen there is a greater degree of wear 31. The second conductor loop 24has a detection portion 32 in a way similar to the first conductor loop23. The detection portion 32 is destroyed when the abrasive disk 2 isworn by more than the distance 30. The sensor 22 detects whether thesecond conductor loop 24 is closed or interrupted. The two conductorloops 23, 24 can be galvanically isolated as shown. The sensor 22 canscan the conductor loops 23, 24 one after the other. With the secondconductor loop 24, three states of wear can be distinguished: low,medium, high. For each of the states of wear, a separate maximum speedcan be defined, and for example stored in the memory 29. The transponder15 transmits a radio signal in which the state of both conductor loops23, 24 is coded, The number of conductor loops 23, 24 may be greaterthan two, e.g., up to ten conductor loops. The sensor 22 and the memory29 need only be scaled accordingly.

FIG. 4 and FIG. 5 show other configurations of the conductor loops, inwhich the conductor loops 33, 34 are galvanically connected. A firstconductor loop 33 is at the smallest distance 27 from the originalperiphery 20. A second conductor loop 24 is at a greater distance 30from the original periphery 20. Their respective detection portions 35,36 are radially offset from one another, as in the first embodiment.

The sensor 22 may for example determine the change in resistance of theconnected conductor loops. The conductor loops 33, 34 form an electricalparallel circuit. With each interrupted conductor loop 33, theresistance value of the parallel circuit increases. The conductor loops33, 34 preferably each have a clearly measurable resistance 37. Theresistance 37 may for example be produced by using graphite instead of ametal for the conductor loops 33, 34.

The sensor 22 may determine the inductance or resonant frequency of theparallel-connected conductor loops 33, 34. The inductance of theparallel circuit decreases with each severed conductor loop 33. Theresonant frequency increases with each separated conductor loop 33. Theparallel-connected conductor loops 33, 34 may be part of an oscillatingcircuit 28 of the sensor 22 or be inductively excited via an oscillatingcircuit 28 of the sensor 22.

1.-14. (canceled)
 15. An abrasive disk, comprising: a first layer; asensor embedded in the first layer, wherein an original periphery of theabrasive disk is detectable by the sensor; wherein the sensor has afirst closed conductor loop which is disposed at a first radial distancefrom the original periphery such that when the original periphery isworn by more than the first radial distance the first closed conductorloop is interrupted; and a transponder, wherein a radio signal isemittable by the transponder which is indicative of whether the firstclosed conductor loop is closed or interrupted.
 16. The abrasive disk asclaimed in claim 15, wherein the sensor has a second closed conductorloop which is disposed at a second radial distance from the originalperiphery that is greater than the first radial distance and wherein theradio signal is indicative of which one of the first closed conductorloop and the second closed conductor loop is interrupted.
 17. Theabrasive disk as claimed in claim 16, wherein the first closed conductorloop and the second closed conductor loop have a different radialextent.
 18. The abrasive disk as claimed in claim 16, wherein the firstclosed conductor loop and the second closed conductor loop have adifferent length.
 19. The abrasive disk as claimed in claim 16, whereinthe first closed conductor loop and the second closed conductor loophave a different electromagnetic resonant frequency.
 20. The abrasivedisk as claimed in claim 16, wherein the first closed conductor loop,the second closed conductor loop, and the transponder are printed on afilm.
 21. The abrasive disk as claimed in claim 15, wherein the sensorhas a memory integrated in the sensor in which a measure of a maximumpermissible rotational speed of the abrasive disk is stored independence on the first closed conductor loop when severed and whereinthe measure of the maximum permissible rotational speed is includable inthe radio signal.
 22. The abrasive disk as claimed in claim 15, whereinthe sensor and the transponder are integrated in a radio-frequencyidentification (RFID) chip.
 23. A hand-held power tool, comprising: theabrasive disk as claimed in claim 15; a holder, wherein the holder holdsthe abrasive disk; an electric motor for rotating the abrasive disk; aspeed control for the electric motor; a communication device, wherein aradio signal emitted by the transponder of the abrasive disk isreceivable by the communication device; and a device controller, whereina speed for the speed control is settable based on a received radiosignal.
 24. The hand-held power tool as claimed in claim 23, wherein thedevice controller sets a nominal speed if the communication device doesnot receive a radio signal.
 25. The hand-held power tool as claimed inclaim 23 further comprising a memory in which a measure of a maximumpermissible rotational speed of the abrasive disk is stored.
 26. Thehand-held power tool as claimed in claim 25, wherein the devicecontroller reads out a list of maximum permissible rotational speeds ofthe abrasive disk stored in the memory.
 27. A control method for thehand-held power tool as claimed in claim 23, comprising the steps of:sending a first inquiry concerning a state of wear of the abrasive disk;and adjusting a rotational speed of the abrasive disk based on areceived radio signal.
 28. The control method for the hand-held powertool as claimed in claim 27, further comprising the steps of: sending asecond inquiry concerning a maximum rotational speed of the abrasivedisk which is indicative of a degree of wear of the abrasive disk andwhich is stored in a memory of the hand-held power tool; and adjustingthe rotational speed of the abrasive disk based on a response to thesecond inquiry.
 29. The abrasive disk as claimed in claim 15 furthercomprising a second layer disposed adjacent to the first layer whereinabrasive grains are embedded in the second layer.
 30. The abrasive diskas claimed in claim 15 wherein abrasive grains are embedded in the firstlayer.